1. Field of the Invention
The present invention relates to a dehydrating system which uses a water separation membrane, and more specifically relates to a dehydrating system designed to appropriately deal with the degradation of the water separation membrane in dehydrating a mixture of water and ethanol or propanol having an azeotropic composition with water, hereinafter referred to as a fluid to be processed.
2. Description of the Related Art
Ethanol has been attracting attention as an alternative energy source to replace oil and has a market size estimated at 55,000,000 kL in 2010. However, to use ethanol as a fuel, ethanol must be dehydrated to at least 99.5 wt % after distillation and purification of a crude product obtained from a biomass source such as corn.
For dehydration, a dilute aqueous solution of ethanol has traditionally been concentrated nearly to the azeotropic point of the ethanol/water system by distilling the solution in a distillation column and then this was dehydrated.
There is a dehydration technique which adds an entrainer and dehydrates by azeotropic distillation. However, this technique has some disadvantages, such as a huge amount of thermal energy required because of the need for a step which subjects a ternary system to azeotropic distillation and recovers the entrainer.
In addition, there is also a dehydration technique in which multiple molecular sieve vessels are arranged in parallel and switches are made between them on a batch basis for dehydration However, this technique also has the problem of high energy consumption required for the regeneration of molecular sieve vessels.
Thus, the use of an element without the above disadvantages, such as a water separation membrane, has been considered (Japanese Patent Application Laid-Open No. 58-21629).
However, if pervaporation (PV) using a water separation membrane unit comprising a water separation membrane is adopted, the water separation membrane unit typically has a service life of about 2 years and requires annual replacement of all the water separation membranes. The water separation membrane unit has the problem of reduced availability of the plant using the unit because of the inevitable downtime of the plant during the replacement.
The present invention has been made in view of the above circumstances and has as an object providing a dehydrating system designed to maintain the availability of a plant equipped with a dehydrating system using a water separation membrane by allowing water separation membrane units to be replaced while the plant is in operation.